Capnography is monitoring of concentration or partial pressure of CO₂ in respiratory gases. It provides information about CO₂ production, pulmonary perfusion, alveolar ventilation, respiratory patterns and elimination of CO₂ from the anesthesia circuit and ventilator. Thus it gives us a rapid and reliable method to detect life threatening conditions such as malposition of tracheal tube, ventilatory failure, circulatory failure and defective breathing circuits. Authors experienced that change of capnogram during off pump coronary artery bypass grafting surgery helped early detecting ruptured bulla and prevented intraopertive or postoperative pneumothorax.